more info you might find helpful:
" Pentax Lens Compatibility Chart
Copyright 2006-2016 Mosphotos.com. All rights reserved.
Pentax bayonet lenses labeled "SMC Pentax" are referred to as "K" lenses in the table below. Other Pentax bayonet lenses have the lens designation as a part of their name as in "SMC Pentax-FA."
Note that "star" lenses work like their "non-star" counterparts: DA* lenses work like DA lenses, FA* like FA, F* like F, A* like A, and M* like M.
Exceptions: FA and F "soft" lenses behave like M lenses in terms of metering.
The Pentax Camera Lens Compatibility Chart
__________________________________________
" Pentax K-Mount Lens Series Explained: The differences between various Pentax lens series
In a nutshell
There are several series of Pentax K-mount lenses; the ones currently being produced include the DA (digital), DA L (cheap digital kit), D FA (full-frame, digital optimized), and FA (full-frame) series. While all Pentax K-mount lenses ever produced are compatible with all current Pentax DSLRs (in some cases with restrictions in that not all exposure modes of the camera are supported by old lenses), there are significant differences between each lens series and each has different features. Furthermore some of the newer lenses do not work with older cameras. We'll be exploring the differences between the various K-mount series lenses in this article "
Pentax K-Mount Lenses Explained: The differences between various Pentax lens series
________________________________________________________________
you can fine reviews of various Pentax and third party lenses by following this link
https://www.pentaxforums.com/lensreviews/
______________________________________________
---------- Post added 05-12-18 at 06:29 ----------
just looked at the series of articles on astrophotography and found this warning:
" Lens Selection
This first point should not be controversial. Do not use a zoom lens for astrophotography. Use a prime lens and use the fastest one that you can get (f/1.4, f/1.7, f/1.8, and f/2 lenses provide the most flexibility). A wide aperture allows you to use slightly slower shutter speeds, and the lack of depth of field is irrelevant. Having a lens that's very sharp close to its maximum aperture is ideal.
Because astrophotography is a game of minutes or hours, a fast, manual-focus prime lens is a great option for astrphotography. Many other Pentax prime lenses are great and my five best Pentax prime lenses for star trails as well as astrophotography are listed below.
But first, why shouldn't you use a zoom lens? A zoom lens adds an element of added motion to a camera in that the zoom could creep during the shot. More importantly, though, zoom lenses are often up to three stops slower than primes, meaning you need to set your ISO three stops higher to obtain the same results. That introduces significant noise. Using a zoom lens increases the likelihood of image quality loss at a time when every factor available to gain image quality should be used fully.
Zoom lenses are also longer than prime lenses. This shifts the camera-lens center of gravity away from the central point in the tripod. The further the camera-lens center of gravity is from the tripod's center, the more likely that the combination could introduce camera shake.
Read more at:
Astrophotography Part 2 of 6: Equipment Selection - Articles and Tips | PentaxForums.com
so perhaps a zoom is not a good idea for that goal???
I never had tried it myself